The present disclosure relates generally to a toner comprising a binder and at least one colorant, wherein the binder is comprised of an amorphous resin and a crystalline sulfonated polyester resin. In particular, the crystalline resin has a melting point of at least 70° C., and a re-crystallization point of at least 47° C.
Toners useful for xerographic applications should possess certain properties related to storage stability and particle size integrity. That is, it is desired to have the particles remain intact and not agglomerate until they are fused on paper. Since environmental conditions vary, the toners also should not substantially agglomerate up to a temperature of from about 50° C. to about 55° C.
The toner composite of resin and colorant should also display acceptable triboelectrification properties which vary with the type of carrier or developer composition. A valuable toner attribute is the relative humidity sensitivity ratio, that is, the ability of a toner to exhibit similar charging behavior at different environmental conditions such as high humidity or low humidity. Typically, the relative humidity sensitivity of toners is considered as the ratio between the toner charge at 80 percent humidity divided by the toner charge at 20 percent humidity. Acceptable values for relative humidity sensitivity of toner vary, and are dependant on the xerographic engine and the environment. Typically, the relative humidity sensitivity ratio of toners is expected to be at least 0.5 and preferably 1.
Another important property for xerographic toner compositions is fusing property on paper. Due to energy conservation measures, and more stringent energy characteristics placed on xerographic engines, such as on xerographic fusers, there is pressure to reduce the fixing temperatures of toners onto paper, such as achieving fixing temperatures of from about 90° C. to about 110° C., to permit less power consumption and allowing the fuser system to possess extended lifetimes.
For a contact fuser, that is, a fuser which is in contact with the paper and the image, the toner should not substantially transfer or offset onto the fuser roller, referred to as hot or cold offset depending on whether the temperature is below the fixing temperature of the paper (cold offset), or whether the toner offsets onto a fuser roller at a temperature above the fixing temperature of the toner (hot offset).
Another desirable characteristic of a toner is sufficient release of the paper image from the fuser roll. For oil containing fuser rolls, the toner may not contain a wax. However, for fusers without oil on the fuser (usually hard rolls), the toner will usually contain a lubricant like a wax to provide release and stripping properties. Thus, a toner characteristic for contact fusing applications is that the fusing latitude, that is, the temperature difference between the fixing temperature and the temperature at which the toner offsets onto the fuser, should be from about 30° C. to about 90° C., and preferably from about 50° C. to about 90° C.
Additionally, depending on the xerographic applications, other toner characteristics may be desired, such as providing high gloss images, such as from about 60 to about 80 Gardner gloss units, especially in pictorial color applications. Other toner characteristics relate to nondocument offset, that is, the ability of paper images not to transfer onto adjacent paper images when stacked up, at a temperature of about 55° C. to about 60° C.; nonvinyl offset properties; high image projection efficiency when fused on transparencies, such as from about 75 to 100 percent projection efficiency and preferably from about 85 to 100 percent projection efficiency. The projection efficiency of toners can be directly related to the transparency of the resin utilized, and clear resins are desired.
Additionally, small sized toner particles, such as from about 3 to about 12 microns, and preferably from about 5 to about 7 microns, are desired, especially in xerographic engines wherein high resolution is a characteristic. Toners with the aforementioned small sizes can be economically prepared by chemical processes, also known as direct or “in situ” toner process, and which process involves the direct conversion of emulsion sized particles to toner composites by aggregation and coalescence, or by suspension, microsuspension or microencapsulation processes.
Low fixing toners comprised of semicrystalline resins are known, such as those disclosed in U.S. Pat. No. 5,166,026. There, toners comprised of a semicrystalline copolymer resin, such as poly(alpha-olefin) copolymer resins, with a melting point of from about 30° C. to about 100° C., and containing functional groups comprising hydroxy, carboxy, amino, amido, ammonium or halo, and pigment particles, are disclosed. Similarly, in U.S. Pat. No. 4,952,477, toner compositions comprised of resin particles selected from the group consisting of a semicrystalline polyolefin and copolymers thereof with a melting point of from about 50° C. to about 100° C. and pigment particles are disclosed. Although it is indicated that some of these toners may provide low fixing temperatures of about 200° F. to about 225° F. using contact fusing applications, the resins are derived from components with melting characteristics of about 30° C. to about 50° C. These resins are not believed to exhibit more desirable melting characteristics, such as about 55° C. to about 60° C.
In U.S. Pat. No. 4,990,424, toners comprised of a blend of resin particles containing styrene polymers or polyesters, and components selected from the group consisting of a semicrystalline polyolefin and copolymers thereof with a melting point of from about 50° C. to about 100° C., are disclosed. Fusing temperatures of from about 250° F. to about 330° F. are reported.
Low fixing crystalline based toners are disclosed in U.S. Pat. No. 6,413,691. There, a toner comprised of a binder resin and a colorant, the binder resin containing a crystalline polyester containing a carboxylic acid of two or more valences having a sulfonic acid group as a monomer component, are illustrated.
Crystalline based toners are disclosed in U.S. Pat. No. 4,254,207. Low fixing toners comprised of crosslinked crystalline resin and amorphous polyester resin are illustrated in U.S. Pat. Nos. 5,147,747 and 5,057,392. In each, the toner powder is comprised, for example, of polymer particles of partially carboxylated crystalline polyester and partially carboxylated amorphous polyester that has been crosslinked together at an elevated temperature with the aid of an epoxy novolac resin and a crosslinking catalyst.
Emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in a number of Xerox patents, the disclosures of which are totally incorporated herein by reference, such as U.S. Pat. Nos. 5,290,654, 5,278,020, 5,308,734, 5,346,797, 5,370,963, 5,344,738, 5,403,693, 5,418,108 and 5,364,729.
Also of interest may be U.S. Pat. Nos. 6,830,860, 6,383,705 and 4,385,107, the disclosures of which are totally incorporated herein by reference.
Existing low melt toners do not meet the heat cohesion requirements when no external additives are added to the toner. The heat cohesion of known low melt toners with no additives is generally greater than 77%. Low melt toners without additives and a heat cohesion of less than 20% are particularly robust. Thus, it is preferred that low melt toners having no external additives have a heat cohesion of less than 20%, and more preferably less than 10%. For comparison, low melt toners having external additives have a heat cohesion of less than 10%.
Toners with low heat cohesion have desired flow characteristics and resist agglomeration or fusing before actually being imaged and fused. Toners must have fluidity or good powder flow such that they are properly imaged in copier/printers. After a toner is manufactured, packaged and shipped, it may encounter temperature variations in environment typically up to 40° C. and in extreme cases as high as 50° C. Under such conditions, if the particle starts to flow (i.e., melt), the particle will stick to other particles and agglomerate and result in poor toner.
There is thus a need to provide low melt toners that may be used at lower fusing temperatures that still provide excellent properties, including excellent document offset and heat cohesion. There is also a need to provide a process for preparing such low melt toners that allows for controlled particle growth and controlled morphology or shape, and provides high yields.